ProjectThe role of three-dimensional genome architecture in antigenic variation

Researcher (PI)Tim Nicolai SIEGEL

Host Institution (HI)LUDWIG-MAXIMILIANS-UNIVERSITAET MUENCHEN

Call DetailsStarting Grant (StG), LS6, ERC-2016-STG

SummaryAntigenic variation is a widely employed strategy to evade the host immune response. It has similar functional requirements even in evolutionarily divergent pathogens. These include the mutually exclusive expression of antigens and the periodic, nonrandom switching in the expression of different antigens during the course of an infection. Despite decades of research the mechanisms of antigenic variation are not fully understood in any organism.
The recent development of high-throughput sequencing-based assays to probe the 3D genome architecture (Hi-C) has revealed the importance of the spatial organization of DNA inside the nucleus. 3D genome architecture plays a critical role in the regulation of mutually exclusive gene expression and the frequency of translocation between different genomic loci in many eukaryotes. Thus, genome architecture may also be a key regulator of antigenic variation, yet the causal links between genome architecture and the expression of antigens have not been studied systematically. In addition, the development of CRISPR-Cas9-based approaches to perform nucleotide-specific genome editing has opened unprecedented opportunities to study the influence of DNA sequence elements on the spatial organization of DNA and how this impacts antigen expression.
I have adapted both Hi-C and CRISPR-Cas9 technology to the protozoan parasite Trypanosoma brucei, one of the most important model organisms to study antigenic variation. These techniques will enable me to bridge the field of antigenic variation research with that of genome architecture. I will perform the first systematic analysis of the role of genome architecture in the mutually exclusive and hierarchical expression of antigens in any pathogen.
The experiments outlined in this proposal will provide new insight, facilitating a new view of antigenic variation and may eventually help medical intervention in T. brucei and in other pathogens relying on antigenic variation for their survival.

Antigenic variation is a widely employed strategy to evade the host immune response. It has similar functional requirements even in evolutionarily divergent pathogens. These include the mutually exclusive expression of antigens and the periodic, nonrandom switching in the expression of different antigens during the course of an infection. Despite decades of research the mechanisms of antigenic variation are not fully understood in any organism.
The recent development of high-throughput sequencing-based assays to probe the 3D genome architecture (Hi-C) has revealed the importance of the spatial organization of DNA inside the nucleus. 3D genome architecture plays a critical role in the regulation of mutually exclusive gene expression and the frequency of translocation between different genomic loci in many eukaryotes. Thus, genome architecture may also be a key regulator of antigenic variation, yet the causal links between genome architecture and the expression of antigens have not been studied systematically. In addition, the development of CRISPR-Cas9-based approaches to perform nucleotide-specific genome editing has opened unprecedented opportunities to study the influence of DNA sequence elements on the spatial organization of DNA and how this impacts antigen expression.
I have adapted both Hi-C and CRISPR-Cas9 technology to the protozoan parasite Trypanosoma brucei, one of the most important model organisms to study antigenic variation. These techniques will enable me to bridge the field of antigenic variation research with that of genome architecture. I will perform the first systematic analysis of the role of genome architecture in the mutually exclusive and hierarchical expression of antigens in any pathogen.
The experiments outlined in this proposal will provide new insight, facilitating a new view of antigenic variation and may eventually help medical intervention in T. brucei and in other pathogens relying on antigenic variation for their survival.

Max ERC Funding

1 498 175 €

Duration

Start date: 2017-04-01, End date: 2022-03-31

Project acronymAIM2 INFLAMMASOME

ProjectCytosolic recognition of foreign nucleic acids: Molecular and functional characterization of AIM2, a central player in DNA-triggered inflammasome activation

Researcher (PI)Veit Hornung

Host Institution (HI)UNIVERSITAETSKLINIKUM BONN

Call DetailsStarting Grant (StG), LS6, ERC-2009-StG

SummaryHost cytokines, chemokines and type I IFNs are critical effectors of the innate immune response to viral and bacterial pathogens. Several classes of germ-line encoded pattern recognition receptors have been identified, which sense non-self nucleic acids and trigger these responses. Recently NLRP-3, a member of the NOD-like receptor (NLR) family, has been shown to sense endogenous danger signals, environmental insults and the DNA viruses adenovirus and HSV. Activation of NLRP-3 induces the formation of a large multiprotein complex in cells termed inflammasome , which controls the activity of pro-caspase-1 and the maturation of pro-IL-1² and pro-IL18 into their active forms. NLRP-3, however, does not regulate these responses to double stranded cytosolic DNA. We identified the cytosolic protein AIM2 as the missing receptor for cytosolic DNA. AIM2 contains a HIN200 domain, which binds to DNA and a pyrin domain, which associates with the adapter molecule ASC to activate both NF-ºB and caspase-1. Knock down of AIM2 down-regulates caspase-1-mediated IL-1² responses following DNA stimulation or vaccinia virus infection. Collectively, these observations demonstrate that AIM2 forms an inflammasome with the DNA ligand and ASC to activate caspase-1. Our underlying hypothesis for this proposal is that AIM2 plays a central role in host-defence to cytosolic microbial pathogens and also in DNA-triggered autoimmunity. The goals of this research proposal are to further characterize the DNA ligand for AIM2, to explore the molecular mechanisms of AIM2 activation, to define the contribution of AIM2 to host-defence against viral and bacterial pathogens and to assess its function in nucleic acid triggered autoimmune disease. The characterization of AIM2 and its role in innate immunity could open new avenues in the advancement of immunotherapy and treatment of autoimmune disease.

Host cytokines, chemokines and type I IFNs are critical effectors of the innate immune response to viral and bacterial pathogens. Several classes of germ-line encoded pattern recognition receptors have been identified, which sense non-self nucleic acids and trigger these responses. Recently NLRP-3, a member of the NOD-like receptor (NLR) family, has been shown to sense endogenous danger signals, environmental insults and the DNA viruses adenovirus and HSV. Activation of NLRP-3 induces the formation of a large multiprotein complex in cells termed inflammasome , which controls the activity of pro-caspase-1 and the maturation of pro-IL-1² and pro-IL18 into their active forms. NLRP-3, however, does not regulate these responses to double stranded cytosolic DNA. We identified the cytosolic protein AIM2 as the missing receptor for cytosolic DNA. AIM2 contains a HIN200 domain, which binds to DNA and a pyrin domain, which associates with the adapter molecule ASC to activate both NF-ºB and caspase-1. Knock down of AIM2 down-regulates caspase-1-mediated IL-1² responses following DNA stimulation or vaccinia virus infection. Collectively, these observations demonstrate that AIM2 forms an inflammasome with the DNA ligand and ASC to activate caspase-1. Our underlying hypothesis for this proposal is that AIM2 plays a central role in host-defence to cytosolic microbial pathogens and also in DNA-triggered autoimmunity. The goals of this research proposal are to further characterize the DNA ligand for AIM2, to explore the molecular mechanisms of AIM2 activation, to define the contribution of AIM2 to host-defence against viral and bacterial pathogens and to assess its function in nucleic acid triggered autoimmune disease. The characterization of AIM2 and its role in innate immunity could open new avenues in the advancement of immunotherapy and treatment of autoimmune disease.

Max ERC Funding

1 727 920 €

Duration

Start date: 2009-12-01, End date: 2014-11-30

Project acronymALLERGUT

ProjectMucosal Tolerance and Allergic Predisposition: Does it all start in the gut?

SummaryCurrently, more than 30% of all Europeans suffer from one or more allergic disorder but treatment is still mostly symptomatic due to a lack of understanding the underlying causality. Allergies are caused by type 2 immune responses triggered by recognition of harmless antigens. Both genetic and environmental factors have been proposed to favour allergic predisposition and both factors have a huge impact on the symbiotic microbiota and the intestinal immune system. Recently we and others showed that the transcription factor ROR(γt) seems to play a key role in mucosal tolerance in the gut and also regulates intestinal type 2 immune responses.
Based on these results I postulate two major events in the gut for the development of an allergy in the lifetime of an individual: First, a failure to establish mucosal tolerance or anergy constitutes a necessity for the outbreak of allergic symptoms and allergic disease. Second, a certain ‘core’ microbiome or pathway of the intestinal microbiota predispose certain individuals for the later development of allergic disorders. Therefore, I will address the following aims:
1) Influence of ROR(γt) on mucosal tolerance induction and allergic disorders
2) Elucidate the T cell receptor repertoire of intestinal Th2 and ROR(γt)+ Tregs and assess the role of alternative NFκB pathway for induction of mucosal tolerance
3) Identification of ‘core’ microbiome signatures or metabolic pathways that favour allergic predisposition
ALLERGUT will provide ground-breaking knowledge on molecular mechanisms of the failure of mucosal tolerance in the gut and will prove if the resident ROR(γt)+ T(reg) cells can function as a mechanistic starting point for molecular intervention strategies on the background of the hygiene hypothesis. The vision of ALLERGUT is to diagnose mucosal disbalance, prevent and treat allergic disorders even before outbreak and thereby promote Public Health initiative for better living.

Currently, more than 30% of all Europeans suffer from one or more allergic disorder but treatment is still mostly symptomatic due to a lack of understanding the underlying causality. Allergies are caused by type 2 immune responses triggered by recognition of harmless antigens. Both genetic and environmental factors have been proposed to favour allergic predisposition and both factors have a huge impact on the symbiotic microbiota and the intestinal immune system. Recently we and others showed that the transcription factor ROR(γt) seems to play a key role in mucosal tolerance in the gut and also regulates intestinal type 2 immune responses.
Based on these results I postulate two major events in the gut for the development of an allergy in the lifetime of an individual: First, a failure to establish mucosal tolerance or anergy constitutes a necessity for the outbreak of allergic symptoms and allergic disease. Second, a certain ‘core’ microbiome or pathway of the intestinal microbiota predispose certain individuals for the later development of allergic disorders. Therefore, I will address the following aims:
1) Influence of ROR(γt) on mucosal tolerance induction and allergic disorders
2) Elucidate the T cell receptor repertoire of intestinal Th2 and ROR(γt)+ Tregs and assess the role of alternative NFκB pathway for induction of mucosal tolerance
3) Identification of ‘core’ microbiome signatures or metabolic pathways that favour allergic predisposition
ALLERGUT will provide ground-breaking knowledge on molecular mechanisms of the failure of mucosal tolerance in the gut and will prove if the resident ROR(γt)+ T(reg) cells can function as a mechanistic starting point for molecular intervention strategies on the background of the hygiene hypothesis. The vision of ALLERGUT is to diagnose mucosal disbalance, prevent and treat allergic disorders even before outbreak and thereby promote Public Health initiative for better living.

Max ERC Funding

1 498 175 €

Duration

Start date: 2017-07-01, End date: 2022-06-30

Project acronymAnti-Virome

ProjectA combined evolutionary and proteomics approach to the discovery, induction and application of antiviral immunity factors

Researcher (PI)Frank Kirchhoff

Host Institution (HI)UNIVERSITAET ULM

Call DetailsAdvanced Grant (AdG), LS6, ERC-2012-ADG_20120314

Summary"Humans are equipped with a variety of intrinsic immunity or host restriction factors. These evolved under positive selection pressure for diversification and represent a first line of defence against invading viruses. Unfortunately, however, many pathogens have evolved effective antagonists against our defences. For example, the capability of HIV-1 to counteract human restriction factors that interfere with reverse transcription, uncoating and virion release has been a prerequisite for the global spread of AIDS. We are just beginning to understand the diversity and induction of antiretroviral factors and how pandemic HIV-1 group M (major) strains evolved to counteract all of them. Here, I propose to use a genetics, proteomics and evolutionary approach to discover and define as-yet-unknown antiviral effectors and their inducers. To identify novel antiviral factors, we will examine the capability of all primate genes that are under strong positive selection pressure to inhibit HIV and its simian (SIV) precursors. This examination from the evolutionary perspective of the invading pathogen will also reveal which adaptations allowed HIV-1 to cause the AIDS pandemic. Furthermore, complex peptide-protein libraries representing essentially the entire human peptidome, will be utilized to identify novel specific inducers of antiviral restriction factors. My ultimate aim is to unravel the network of inducers and effectors of antiviral immunity - the ""Anti-Virome"" - and to use this knowledge to develop novel effective preventive and therapeutic approaches based on the induction of combinations of antiviral factors targeting different steps of the viral life cycle. The results of this innovative and interdisciplinary program will provide fundamental new insights into intrinsic immunity and may offer alternatives to conventional vaccine and therapeutic approaches because most restriction factors have broad antiviral activity and are thus effective against various pathogens."

"Humans are equipped with a variety of intrinsic immunity or host restriction factors. These evolved under positive selection pressure for diversification and represent a first line of defence against invading viruses. Unfortunately, however, many pathogens have evolved effective antagonists against our defences. For example, the capability of HIV-1 to counteract human restriction factors that interfere with reverse transcription, uncoating and virion release has been a prerequisite for the global spread of AIDS. We are just beginning to understand the diversity and induction of antiretroviral factors and how pandemic HIV-1 group M (major) strains evolved to counteract all of them. Here, I propose to use a genetics, proteomics and evolutionary approach to discover and define as-yet-unknown antiviral effectors and their inducers. To identify novel antiviral factors, we will examine the capability of all primate genes that are under strong positive selection pressure to inhibit HIV and its simian (SIV) precursors. This examination from the evolutionary perspective of the invading pathogen will also reveal which adaptations allowed HIV-1 to cause the AIDS pandemic. Furthermore, complex peptide-protein libraries representing essentially the entire human peptidome, will be utilized to identify novel specific inducers of antiviral restriction factors. My ultimate aim is to unravel the network of inducers and effectors of antiviral immunity - the ""Anti-Virome"" - and to use this knowledge to develop novel effective preventive and therapeutic approaches based on the induction of combinations of antiviral factors targeting different steps of the viral life cycle. The results of this innovative and interdisciplinary program will provide fundamental new insights into intrinsic immunity and may offer alternatives to conventional vaccine and therapeutic approaches because most restriction factors have broad antiviral activity and are thus effective against various pathogens."

Max ERC Funding

1 915 200 €

Duration

Start date: 2013-04-01, End date: 2018-03-31

Project acronymARCHAELLUM

ProjectAssembly and function of the crenarchaeal flagellum

Researcher (PI)Sonja-Verena Albers

Host Institution (HI)ALBERT-LUDWIGS-UNIVERSITAET FREIBURG

Call DetailsStarting Grant (StG), LS6, ERC-2012-StG_20111109

Summary"Archaea constitute the third domain of life and are believed to be close to the origin of life. They comprise a diverse group of micro-organisms that combine bacterial and eukaryotic features, but also employ many novel mechanisms. They possess a unique cell envelope with a cytoplasmic membrane of ether lipids surrounded by a proteinaceous S-layer and various cell appendages such as flagella, pili and more unusual structures. Studies have shown that the archaeal flagellum is an unique structure as it functionally resembles the bacterial flagellum, but structurally it is a simple type IV pilus. Moreover, we have shown that this type IV pilus can rotate. Therefore I propose to name the archaeal flagellum, the archaellum, as it is fundamentally different from the bacterial flagellum.
In this proposal I aim to understand the assembly and mechanism of rotation of the archaellum of the thermocacidophilic crenarchaen Sulfolobus acidocaldarius by using biochemical, genetic and biophysical methods. The main milestons are:
- Biochemical and structural characterization of all archaellum subunits
- To understand the assembly pathway of the archaellum and the interactions of its different
subunits
- To understand how rotation of the filament is achieved and which subunits are important
for this movement
This work will identify a new, relatively simple motor complex that has evolved from primordial type IV pili assembly machineries and therefore uncover general principles of macromolecular assemblies at cellular surfaces and a novel mechanism to generate mechanical force that can be translated into movement."

"Archaea constitute the third domain of life and are believed to be close to the origin of life. They comprise a diverse group of micro-organisms that combine bacterial and eukaryotic features, but also employ many novel mechanisms. They possess a unique cell envelope with a cytoplasmic membrane of ether lipids surrounded by a proteinaceous S-layer and various cell appendages such as flagella, pili and more unusual structures. Studies have shown that the archaeal flagellum is an unique structure as it functionally resembles the bacterial flagellum, but structurally it is a simple type IV pilus. Moreover, we have shown that this type IV pilus can rotate. Therefore I propose to name the archaeal flagellum, the archaellum, as it is fundamentally different from the bacterial flagellum.
In this proposal I aim to understand the assembly and mechanism of rotation of the archaellum of the thermocacidophilic crenarchaen Sulfolobus acidocaldarius by using biochemical, genetic and biophysical methods. The main milestons are:
- Biochemical and structural characterization of all archaellum subunits
- To understand the assembly pathway of the archaellum and the interactions of its different
subunits
- To understand how rotation of the filament is achieved and which subunits are important
for this movement
This work will identify a new, relatively simple motor complex that has evolved from primordial type IV pili assembly machineries and therefore uncover general principles of macromolecular assemblies at cellular surfaces and a novel mechanism to generate mechanical force that can be translated into movement."

SummaryThe proposed project aims at investigating the molecular mechanisms that activate B cell antigen receptor (BCR) signalling in chronic lymphocytic leukaemia (CLL). While it is widely accepted that the unbroken BCR expression in CLL cells is indicative for a key role in disease development, the mechanisms that induce BCR activation and survival of malignant cells are still elusive. Using a unique reconstitution system, we have recently shown that CLL-derived BCRs possess the exceptional capacity for cell-autonomous signalling independent of external antigen. Crystallographic analyses confirmed our model that CLL-BCRs bind to intrinsic motifs in nearby BCRs on the very same cell. In addition to the BCR, several pathogenic factors influence the biological behaviour of CLL cells, but the functional hierarchy and the effect on BCR signalling are insufficiently understood. Here, we aim at investigating the structural cause of autonomous signalling as well as the characterization of important signalling pathways and their mechanistic action in CLL pathogenesis.
By combining crystallography with the measurement of autonomous signalling of wild type and mutated receptors in our unique reconstitution system, we will generate a structure-function relationship for CLL-BCRs. By generating new animal models and by employing classical as well as cutting-edge approaches of biochemistry and molecular/cellular immunology, we will comprehensively characterize the signalling pathways that are activated by autonomous signalling and might be important for CLL pathogenesis.
These systematic efforts are necessary to understand how various biological mechanisms operate and ultimately activate downstream pathways that result in a lymphoproliferative disease. In addition, a cohesive model of CLL pathogenesis, which elucidates the hierarchical order of pathogenic factors and their interaction with BCR signalling, may well lead to novel disease-specific preventive or therapeutic intervention.

The proposed project aims at investigating the molecular mechanisms that activate B cell antigen receptor (BCR) signalling in chronic lymphocytic leukaemia (CLL). While it is widely accepted that the unbroken BCR expression in CLL cells is indicative for a key role in disease development, the mechanisms that induce BCR activation and survival of malignant cells are still elusive. Using a unique reconstitution system, we have recently shown that CLL-derived BCRs possess the exceptional capacity for cell-autonomous signalling independent of external antigen. Crystallographic analyses confirmed our model that CLL-BCRs bind to intrinsic motifs in nearby BCRs on the very same cell. In addition to the BCR, several pathogenic factors influence the biological behaviour of CLL cells, but the functional hierarchy and the effect on BCR signalling are insufficiently understood. Here, we aim at investigating the structural cause of autonomous signalling as well as the characterization of important signalling pathways and their mechanistic action in CLL pathogenesis.
By combining crystallography with the measurement of autonomous signalling of wild type and mutated receptors in our unique reconstitution system, we will generate a structure-function relationship for CLL-BCRs. By generating new animal models and by employing classical as well as cutting-edge approaches of biochemistry and molecular/cellular immunology, we will comprehensively characterize the signalling pathways that are activated by autonomous signalling and might be important for CLL pathogenesis.
These systematic efforts are necessary to understand how various biological mechanisms operate and ultimately activate downstream pathways that result in a lymphoproliferative disease. In addition, a cohesive model of CLL pathogenesis, which elucidates the hierarchical order of pathogenic factors and their interaction with BCR signalling, may well lead to novel disease-specific preventive or therapeutic intervention.

Max ERC Funding

2 256 250 €

Duration

Start date: 2016-11-01, End date: 2021-10-31

Project acronymBaby DCs

ProjectAge-dependent Regulation of Dendritic Cell Development and Function

Researcher (PI)Barbara Ursula SCHRAML

Host Institution (HI)LUDWIG-MAXIMILIANS-UNIVERSITAET MUENCHEN

Call DetailsStarting Grant (StG), LS6, ERC-2016-STG

SummaryEarly life immune balance is essential for survival and establishment of healthy immunity in later life. We aim to define how age-dependent regulation of dendritic cell (DC) development contributes to this crucial immune balance. DCs are versatile controllers of immunity that in neonates are qualitatively distinct from adults. Why such age-dependent differences exist is unclear but newborn DCs are considered underdeveloped and functionally immature.
Using ontogenetic tracing of conventional DC precursors, I have found a previously unappreciated developmental heterogeneity of DCs that is particularly prominent in young mice. Preliminary data indicate that distinct waves of DC poiesis contribute to the functional differences between neonatal and adult DCs. I hypothesize that the neonatal DC compartment is not immature but rather that DC poiesis is developmentally regulated to create essential age-dependent immune balance. Further, I have identified a unique situation in early life to address a fundamental biological question, namely to what extent cellular function is pre-programmed by developmental origin (nature) versus environmental factors (nurture).
In this proposal, we will first use novel models to fate map the origin of the DC compartment with age. We will then define to what extent cellular origin determines age-dependent functions of DCs in immunity. Using innovative comparative gene expression profiling and integrative epigenomic analysis the cell intrinsic mechanisms regulating the age-dependent functions of DCs will be characterized. Because environmental factors in utero and after birth critically influence immune balance, we will finally define the impact of maternal infection and metabolic disease, as well as early microbial encounter on DC poiesis. Characterizing how developmentally regulated DC poiesis shapes the unique features of early life immunity will provide novel insights into immune development that are vital to advance vaccine strategies.

Early life immune balance is essential for survival and establishment of healthy immunity in later life. We aim to define how age-dependent regulation of dendritic cell (DC) development contributes to this crucial immune balance. DCs are versatile controllers of immunity that in neonates are qualitatively distinct from adults. Why such age-dependent differences exist is unclear but newborn DCs are considered underdeveloped and functionally immature.
Using ontogenetic tracing of conventional DC precursors, I have found a previously unappreciated developmental heterogeneity of DCs that is particularly prominent in young mice. Preliminary data indicate that distinct waves of DC poiesis contribute to the functional differences between neonatal and adult DCs. I hypothesize that the neonatal DC compartment is not immature but rather that DC poiesis is developmentally regulated to create essential age-dependent immune balance. Further, I have identified a unique situation in early life to address a fundamental biological question, namely to what extent cellular function is pre-programmed by developmental origin (nature) versus environmental factors (nurture).
In this proposal, we will first use novel models to fate map the origin of the DC compartment with age. We will then define to what extent cellular origin determines age-dependent functions of DCs in immunity. Using innovative comparative gene expression profiling and integrative epigenomic analysis the cell intrinsic mechanisms regulating the age-dependent functions of DCs will be characterized. Because environmental factors in utero and after birth critically influence immune balance, we will finally define the impact of maternal infection and metabolic disease, as well as early microbial encounter on DC poiesis. Characterizing how developmentally regulated DC poiesis shapes the unique features of early life immunity will provide novel insights into immune development that are vital to advance vaccine strategies.

Max ERC Funding

1 500 000 €

Duration

Start date: 2017-06-01, End date: 2022-05-31

Project acronymBARCODED-CELLTRACING

ProjectEndogenous barcoding for in vivo fate mapping of lineage development in the blood and immune system

Researcher (PI)Hans-Reimer RODEWALD

Host Institution (HI)DEUTSCHES KREBSFORSCHUNGSZENTRUM HEIDELBERG

Call DetailsAdvanced Grant (AdG), LS6, ERC-2016-ADG

SummaryThe immune system is a complex ensemble of diverse lineages. Studies on in-vivo-hematopoiesis have until
now largely rested on transplantation. More physiological experiments have been limited by the inability to
analyze hematopoietic stem (HSC) and progenitor cells in situ without cell isolation and other disruptive
manipulations. We have developed mouse mutants in which a fluorescent marker can be switched on in HSC
in situ (inducible fate mapping), and traced HSC lineage output under unperturbed conditions in vivo. These
experiments uncovered marked differences comparing in situ and post-transplantation hematopoiesis. These
new developments raise several important questions, notably on the developmental fates HSC realize in vivo
(as opposed to their experimental potential), and on the structure (routes and nodes) of hematopoiesis from
HSC to peripheral blood and immune lineages. Answers to these questions (and in fact the deconvolution of
any tissue) require the development of non-invasive, high resolution barcoding systems. We have now
designed, built and tested a DNA-based barcoding system, termed Polylox, that is based on an artificial
recombination locus in which Cre recombinase can generate several hundred thousand genetic tags in mice.
We chose the Cre-loxP system to link high resolution barcoding (i.e. the ability to barcode single cells and to
fate map their progeny) to the zoo of tissue- or stage-specific, inducible Cre-driver mice. Here, I will present
the principles of this endogenous barcoding system, demonstrate its experimental and analytical feasibilities
and its power to resolve complex lineages. The work program addresses in a comprehensive manner major
open questions on the structure of the hematopoietic system that builds and maintains the immune system.
This project ultimately aims at an in depth dissection of unique or common lineage pathways emerging from
HSC, and at resolving relationships within cell lineages of the immune system.

The immune system is a complex ensemble of diverse lineages. Studies on in-vivo-hematopoiesis have until
now largely rested on transplantation. More physiological experiments have been limited by the inability to
analyze hematopoietic stem (HSC) and progenitor cells in situ without cell isolation and other disruptive
manipulations. We have developed mouse mutants in which a fluorescent marker can be switched on in HSC
in situ (inducible fate mapping), and traced HSC lineage output under unperturbed conditions in vivo. These
experiments uncovered marked differences comparing in situ and post-transplantation hematopoiesis. These
new developments raise several important questions, notably on the developmental fates HSC realize in vivo
(as opposed to their experimental potential), and on the structure (routes and nodes) of hematopoiesis from
HSC to peripheral blood and immune lineages. Answers to these questions (and in fact the deconvolution of
any tissue) require the development of non-invasive, high resolution barcoding systems. We have now
designed, built and tested a DNA-based barcoding system, termed Polylox, that is based on an artificial
recombination locus in which Cre recombinase can generate several hundred thousand genetic tags in mice.
We chose the Cre-loxP system to link high resolution barcoding (i.e. the ability to barcode single cells and to
fate map their progeny) to the zoo of tissue- or stage-specific, inducible Cre-driver mice. Here, I will present
the principles of this endogenous barcoding system, demonstrate its experimental and analytical feasibilities
and its power to resolve complex lineages. The work program addresses in a comprehensive manner major
open questions on the structure of the hematopoietic system that builds and maintains the immune system.
This project ultimately aims at an in depth dissection of unique or common lineage pathways emerging from
HSC, and at resolving relationships within cell lineages of the immune system.

SummaryAcute inflammation is a response to infection or tissue damage that is critical for host protection and tissue homeostasis. However, deregulated or chronic inflammation is harmful to the host and can cause multiple diseases including inflammatory bowel disease, rheumatoid arthritis, cardiovascular diseases, neuroinflammatory disease and cancer. Cells of the innate immune system sense microbial or sterile danger via pattern recognition receptors (PRRs). Subsequently, these PRRs engage intracellular signalling modules to elicit inflammatory effector mechanisms. We have recently identified the CARD9 / BCL10 / MALT1 (CBM) signalosome as a central proinflammatory signalling complex in innate immune cells. This molecular platform responds to stimuli from transmembrane SYK-coupled C-type lectin receptors and from intracellular danger sensors such as RIG-I-like helicases, NOD2 and presumably others to robustly activate NF-κB and MAPK pathways. Innate CBM signalling is engaged upon fungal, bacterial or viral recognition and upon sterile cell injury and it is essential for host protection in humans and mice. Still, it is unclear how the CARD9 / BCL10 / MALT1 signalosome is activated on a molecular level and how CBM responses are transduced to effector cascades. Moreover, although CARD9 polymorphisms are linked to various human inflammatory diseases, the cell type- and signal-specific roles of CBM signalosomes in complex diseases in vivo are unknown. Here we aim to take an integrated genetic, biochemical and in vivo approach to comprehensively dissect the regulation of the CARD9 / BCL10 / MALT1 complex in innate immunity and to define the role of this signalosome in clinically relevant inflammatory diseases. Mechanistic in vitro studies will be combined with the in vivo analysis of CBM function in genetically defined mouse models to gain better insights into the regulation of innate immunity and to pave the way to novel therapeutics for inflammatory diseases.

Acute inflammation is a response to infection or tissue damage that is critical for host protection and tissue homeostasis. However, deregulated or chronic inflammation is harmful to the host and can cause multiple diseases including inflammatory bowel disease, rheumatoid arthritis, cardiovascular diseases, neuroinflammatory disease and cancer. Cells of the innate immune system sense microbial or sterile danger via pattern recognition receptors (PRRs). Subsequently, these PRRs engage intracellular signalling modules to elicit inflammatory effector mechanisms. We have recently identified the CARD9 / BCL10 / MALT1 (CBM) signalosome as a central proinflammatory signalling complex in innate immune cells. This molecular platform responds to stimuli from transmembrane SYK-coupled C-type lectin receptors and from intracellular danger sensors such as RIG-I-like helicases, NOD2 and presumably others to robustly activate NF-κB and MAPK pathways. Innate CBM signalling is engaged upon fungal, bacterial or viral recognition and upon sterile cell injury and it is essential for host protection in humans and mice. Still, it is unclear how the CARD9 / BCL10 / MALT1 signalosome is activated on a molecular level and how CBM responses are transduced to effector cascades. Moreover, although CARD9 polymorphisms are linked to various human inflammatory diseases, the cell type- and signal-specific roles of CBM signalosomes in complex diseases in vivo are unknown. Here we aim to take an integrated genetic, biochemical and in vivo approach to comprehensively dissect the regulation of the CARD9 / BCL10 / MALT1 complex in innate immunity and to define the role of this signalosome in clinically relevant inflammatory diseases. Mechanistic in vitro studies will be combined with the in vivo analysis of CBM function in genetically defined mouse models to gain better insights into the regulation of innate immunity and to pave the way to novel therapeutics for inflammatory diseases.

SummaryLeukocytes are the key components of the immune system that fight infections and provide tissue repair, yet their migration patterns throughout the body over the course of a day are completely unknown. Circadian, ~24 hour rhythms are emerging as important novel regulators of immune cell migration and function, which impacts inflammatory diseases such as myocardial infarction and sepsis. Altering leukocyte tissue infiltration and activation at the proper times provides an option for therapy that would maximize the clinical impact of drugs and vaccinations and minimize side effects.
We aim to create a four-dimensional map of leukocyte migration to organs in time and space and investigate with epigenetics techniques the molecular mechanisms that regulate cell-type specific rhythms. We will functionally define the daily oscillating molecular signature(s) of leukocytes and endothelial cells with novel proteomics approaches and thus identify a circadian traffic code that dictates the rhythmic migration of leukocyte subsets to specific organs under steady-state and inflammatory conditions with pharmacological and genetic tools. We will assess the impact of lineage-specific arrhythmicities on immune homeostasis and leukocyte trafficking using an innovative combination of novel genetic tools. Based on these data we will create a model predicting circadian leukocyte migration to tissues.
The project combines the disciplines of immunology and chronobiology by obtaining unprecedented information in time and space of circadian leukocyte trafficking and investigating how immune-cell specific oscillations are generated at the molecular level, which is of broad impact for both fields. Our extensive experience in the rhythmic control of the immune system makes us well poised to characterize the molecular components that orchestrate circadian leukocyte distribution across the body.

Leukocytes are the key components of the immune system that fight infections and provide tissue repair, yet their migration patterns throughout the body over the course of a day are completely unknown. Circadian, ~24 hour rhythms are emerging as important novel regulators of immune cell migration and function, which impacts inflammatory diseases such as myocardial infarction and sepsis. Altering leukocyte tissue infiltration and activation at the proper times provides an option for therapy that would maximize the clinical impact of drugs and vaccinations and minimize side effects.
We aim to create a four-dimensional map of leukocyte migration to organs in time and space and investigate with epigenetics techniques the molecular mechanisms that regulate cell-type specific rhythms. We will functionally define the daily oscillating molecular signature(s) of leukocytes and endothelial cells with novel proteomics approaches and thus identify a circadian traffic code that dictates the rhythmic migration of leukocyte subsets to specific organs under steady-state and inflammatory conditions with pharmacological and genetic tools. We will assess the impact of lineage-specific arrhythmicities on immune homeostasis and leukocyte trafficking using an innovative combination of novel genetic tools. Based on these data we will create a model predicting circadian leukocyte migration to tissues.
The project combines the disciplines of immunology and chronobiology by obtaining unprecedented information in time and space of circadian leukocyte trafficking and investigating how immune-cell specific oscillations are generated at the molecular level, which is of broad impact for both fields. Our extensive experience in the rhythmic control of the immune system makes us well poised to characterize the molecular components that orchestrate circadian leukocyte distribution across the body.